138 Annals of the South African Museum. 



margin marks the posterior limit of a weakly defined postero- 

 superior area of the valve-surface. This is only demarcated from the 

 flank by a weak and flattened fold of the surface which passes 

 obliquely backwards from the umbo to the postero-inferior angle of 

 the valve. 



The ornamentation consists of very delicate, closely spaced, 

 rounded, concentric ridges, separated by impressed linear interspaces. 

 The ridges traverse the flank, parallel to the pallial border, then turn 

 sharply upwards to cross the area in a direction parallel with the 

 siphonal border. On the area the ornaments are slightly coarser 

 and less regular, and less strongly developed than on the flank. 



An internal cast of a left valve shows traces of very weak rounded 

 ribbing, running parallel to the inferior border, but these markings 

 are confined to the middle part of the valve and terminate posteriorly 

 at the oblique, weak carinal ridge. In addition to the two short, 

 diverging, cardinal teeth, there are indications of a narrow, lath-like 

 ridge (represented on the cast by a narrow hollow) running parallel 

 with the upper valve-margin for a short distance in front of the 

 umbo, and another similar narrow depression extends for a longer 

 distance close to the valve-margin behind the umbo. Just above the 

 posterior part of the broadly oval anterior adductor impression, 

 is a small, well-marked, oval pedal muscle-scar. The somewhat 

 elongated posterior adductor impression is situated close to the upper 

 valve-border, half-way between the umbo and the posterior margin, 

 and just below the narrow, lath-like process which is represented on 

 the cast by a groove close to j the valve-margin. The pallial line on 

 reaching its posterior extremity turns sharply forward with an 

 angular bend. 



Dimensions. (1) (2) 



Length 15 , 22 mm. 



Greatest height 8 . 12 ,, 



Occurrence. Specimen (1), preserved as a mould of the external 

 surface of a left valve, was found on the left side of the Coega 

 Valley, half a mile down from the railway (461g). Specimen (2), 

 which is the cast of the interior of a left valve, came from a bare 

 slope W. 30 S. from the middle of Barkly Bridge, on the farm 

 Olif ant's Kop, Sunday's Eiver (35h). 



Remarks. There can be no reasonable doubt that the two 

 specimens above described, showing the exterior and interior 

 characters respectively, belong to one species. They are of interest 

 as representing a genus of shells which is elsewhere only known to 

 occur in rocks of Cretaceous age. These valves have a very delicately 



